Maquetación 1

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Maquetación 1

Articulo 9_ART. El material tipo de la 25/06/15 08:19 Página 483
Vázquez, J.T., Alonso, B., Fernández-Puga, M.C., Gómez-Ballesteros, M., Iglesias, J., Palomino, D., Roque, C., Ercilla, G. and Díaz-del-Río, V., 2015. Seamounts
along the Iberian Continental Margins. Boletín Geológico y Minero, 126 (2-3): 483-514
ISSN: 0366-0176
Seamounts along the Iberian continental margins
J.T. Vázquez(1), B. Alonso(2), M. C. Fernández-Puga(3), M. Gómez-Ballesteros(4), J. Iglesias(5), D. Palomino(1),
C. Roque(6), G. Ercilla(2) and V. Díaz-del-Río(1)
(1) Instituto Español de Oceanografía. Centro Oceanográfico de Málaga, Puerto Pesquero s/n, 29640, Fuengirola, Spain.
[email protected]; [email protected]; [email protected]
(2) Institut de Ciències del Mar, CSIC. Passeig Marítim de la Barceloneta, 37-49. 08003, Barcelona, Spain.
[email protected]; [email protected]
(3) Departamento de Ciencias de la Tierra, Facultad de Ciencias del Mar y Ambientales, Universidad de Cádiz,
Campus de Puerto Real, 11510, Puerto Real, Spain.
[email protected]
(4) Instituto Español de Oceanografía. Sede Central de Madrid, C/ Corazón de María 8, 28002, Madrid, Spain.
[email protected]
(5) IPROMA S.L., Camiño vello de Santiago n°24 - 36419, Sanguiñeda – Mos, Pontevedra, Spain.
[email protected]
(6) Instituto Português do Mar e da Atmosfera, 1749-077, Lisboa, Portugal.
[email protected]
ABSTRACT
Seamounts are first-order morphological elements on continental margins and in oceanic domains, which
have been extensively researched over recent decades in all branches of oceanography. These features
favour the development of several geological processes, and their study gives us a better understanding of
their geological and morphological domains. The seamounts around Iberia are numerous and provide excellent examples of the geodiversity of these morphological elements. Here we present a compilation of 15
seamounts around the Iberian Peninsula. These seamounts have different origins related to the geodynamic
evolution (volcanism, extensional or compressive tectonics, and diapirism) of the domains where they are
located. The current configuration of their relief has been influenced by Neogene-Quaternary tectonics. Their
positioning controls the current morpho-sedimentary processes in the basins and on the margins, and highlights the fact that downslope processes on seamount flanks (mass flows, turbidite flows, and landslides) and
processes parallel to seamounts (contouritic currents) correspond to the major geological features they are
associated with them. Biogenic structures commonly develop on the tops of seamounts where occasionally
isolated shelves form that have carbonate-dominated sedimentation.
Key words: Iberia, morphology, seamounts, sedimentary environments, tectonics.
Los montes submarinos en los márgenes continentales de Iberia
RESUMEN
Los montes submarinos son rasgos morfológicos singulares, cuyo estudio tiene gran relevancia desde el
punto de vista de las distintas ramas de la oceanografía. Su presencia favorece el desarrollo de diferentes
procesos geológicos y proporciona un mejor conocimiento de los dominios geológicos y morfológicos en los
que se encuentran. En el entorno de Iberia, los montes submarinos tienen una amplia representación y tipología. En este trabajo, se presenta una recopilación geológica de 15 montes submarinos (ocho en el Mar
Mediterráneo y siete en el Océano Atlántico) de los márgenes continentales de Iberia y en el dominio
Oceánico Atlántico, utilizándose levantamientos batimétricos y geofísicos. El origen de estos montes es muy
diferente y está relacionado con la evolución geodinámica del dominio geológico en el que aparecen (volcanismo, tectónica extensional o compresional y diapirismo). La configuración actual del relieve ha sido controlada por la actividad tectónica en el Neógeno-Cuaternario. Su presencia controla el desarrollo de los procesos morfosedimentarios recientes de márgenes y cuencas. Los principales procesos sedimentarios
asociados a estos montes se relacionan con procesos longitudinales (flujos en masa, flujos turbidíticos, deslizamientos) y transversales a dichos montes (corrientes de contorno). Además es frecuente en ellos el desarrollo de cuerpos biogénicos sobre sus cimas e incluso de plataformas con sedimentación carbonatada. Los
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Vázquez, J.T. et al., 2015. Seamounts along the Iberian Continental Margins. Boletín Geológico y Minero, 126 (2-3): 483-514
montes submarinos de Iberia muestran una gran geodiversidad y constituyen un elemento morfológico de
primer orden para comprender los procesos geológicos que tienen lugar en sus márgenes continentales y
dominios oceánicos adyacentes.
Palabras clave: Iberia, morfología, montes submarinos, ambientes sedimentarios, tectónica.
VERSION ABREVIADA EN CASTELLANO
Introducción
Los montes submarinos (MS) son rasgos morfológicos que se elevan sobre los fondos adyacentes con desniveles superiores a 1.000 m, y pueden aparecer como montañas aisladas o formando cadenas de montes.
En sentido amplio también se consideran elevaciones menores (colinas) con desniveles inferiores a 1.000 m.
Recientemente existe la tendencia de englobar dentro del concepto de monte submarino todas las elevaciones sobre los fondos marinos que alcancen al menos 100 m de relieve sobre los fondos adyacentes. Se trata
de elementos singulares del relieve submarino que tienen gran relevancia en las diferentes disciplinas de la
oceanografía. Desde el punto de vista geológico, la caracterización y distribución de los montes submarinos
ha permitido una mejor comprensión de la evolución del fondo de los océanos, de las dorsales oceánicas y
de la tectónica de placas, así como un incremento del conocimiento de los procesos geológicos (tectónicos,
sedimentarios) de cada región.
Los montes submarinos en torno a Iberia se localizan en los márgenes continentales de Iberia, y dominios
oceánicos adyacentes. Se han identificado 51 montes submarinos, si bien existen otros muchos de menores
dimensiones (Fig. 1). Los estudios sistemáticos de la geología y oceanografía (Fig. 2) de estos montes son
escasos exceptuando aquellos trabajos realizados en el marco de proyectos para caracterizar la Zona
Económica Exclusiva y la Plataforma Continental de España y Portugal, o de caladeros pesqueros. Este trabajo tiene por objetivo la realización de un catálogo geológico de los montes submarinos del entorno de
Iberia, representando su geodiversidad, si bien esta recopilación nace con la vocación del inicio de un catálogo futuro más completo.
Descripción de los montes submarinos: Geomorfología
Se han seleccionado 15 montes submarinos de entre los 51 identificados (números del 1 al 51 de la Fig. 1)
entorno a Iberia en base a sus dimensiones, relevancia científica, nivel de conocimiento y a su inclusión en
propuestas de “Áreas Protegidas Marinas” (Fig. 1 y Tabla 1): en el noreste de Iberia los Montes submarinos
de Ses Olives (6), Ausiàs March (7) y Emilie Baudot (8), localizados en el Promontorio Balear (Fig. 3); en el
sureste de Iberia la Dorsal de Alborán (13) y los montes submarinos de Avempace (14.1), Herradura (14.2),
Herradura Spur (14.3) y Djibouti Ville (14.4) (Bancos de Djibouti), situados en el Mar de Alborán (Figs. 4 y 5);
en el suroeste de Iberia los Bancos de Guadalquivir (27) y Portimao (28), localizados en el Golfo de Cádiz (Figs.
6 y 7); en el dominio atlántico al oeste de Iberia el Monte de Coral Patch (29) situado en la placa de África y
separa las llanuras abisales de Sena y La Herradura, el Banco de Gorringe (31) localizado en la prolongación
suroccidental del margen continental del suroeste de Portugal que separa las llanuras abisales de La
Herradura y del Tajo, y el Monte de Tore (33) que separa las llanuras abisales del Tajo y de Iberia (Fig. 8); al
noroeste de Iberia el Banco de Galicia (36) localizado en el dominio distal del margen continental de Galicia
(Fig. 9); y al norte de Iberia el Banco Le Danois (40) situado en el margen Cantábrico (Fig. 10).
Los montes submarinos estudiados están localizados en un amplio rango de profundidades (20-5.200 m),
con pendientes suaves en sus cumbres (0.3-3°) y elevadas en sus flancos (hasta 53°) (Tabla 1). Presentan gran
diversidad de tipos morfológicos y sedimentarios que se agrupan en siete tipos (Figs. 3 a 10): i) estructurales
(escarpes, crestas, altos, fallas), ii) volcánicos, iii) de dinámica de fluidos (estructuras de colapso, ondulaciones y pockmarks), iv) de movimientos en masa (cárcavas, canales, deslizamientos, depósitos de derrubios),
v) de corrientes de fondo (surcos, canales, ondas de sedimento, depósitos contorníticos y terrazas); vi) biogénicos y vii) mixtas, incluyendo fondos de “maërl” (acumulaciones de algas rojas cálcareas) en plataformas
aisladas.
Procesos genéticos
La formación de los montes submarinos de Ses Olives y Ausiàs March (Fig. 3) se relaciona con la compartimentación del borde meridional del Promontorio Balear, generado durante la apertura del Mediterráneo
Occidental a lo largo del Mioceno. Este proceso tectónico desarrolló sistemas de fallas normales de dirección
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NE-SO, entre las que destaca el límite suroriental del promontorio conocido como escarpe Emile Baudot. El
monte de Emile Baudot (Fig. 3), situado sobre la parte superior de este escarpe, es un “guyot” que presenta
la misma orientación y se formó en la prolongación de la sierra meridional de la isla de Mallorca, además ha
sido inyectado por estructuras volcánicas. Los montes submarinos estudiados del Mar de Alborán fueron inicialmente altos estructurales y/o volcánicos formados durante la extensión transarco de la cuenca (Oligoceno
superior-Mioceno) (Figs. 4 y 5), si bien su actual relieve es consecuencia de la reactivación tectónica compresiva de estos altos durante el Plioceno-Cuaternario. Los montes submarinos del Golfo de Cádiz (Figs. 6 y
7), fueron inicialmente altos estructurales de basamento en el contexto de un margen continental transformante (Triásico-Cretácico inferior), si bien su última elevación se ha producido durante el emplazamiento de
las unidades Béticas en el Mioceno y la reactivación de todo el sistema durante el Plioceno-Cuaternario. En
el dominio atlántico del oeste de Iberia, el monte submarino de Coral Patch está formado por actividad magmática en el Eoceno, en relación con la traza del punto caliente de Madeira; el Banco de Gorringe se relaciona con el desarrollo del margen transformante Suribérico durante la apertura de la cuenca del Atlántico
Central; y el Monte submarino de Tore se debe al emplazamiento de crestas volcánicas alcalinas en el
Cretácico superior, si bien el relieve de todas estas estructuras se han realzado como resultado de la actividad tectónica durante la compresión alpina (Fig. 8). El Banco de Galicia es un “horst” tectónico formado
durante la fracturación extensional del margen en el Mesozoico (Fig. 9), si bien el patrón actual del relieve se
ha interpretado con una reactivación de la fracturación y abovedamiento causado por la elevación del margen durante la orogenia Alpina. El Banco Le Danois fue producido por la inversión y levantamiento del margen que tuvo lugar durante la compresión del Terciario (Fig. 10) previamente fracturado durante la etapa de
rifting Mesozoico.
Procesos geológicos asociados
Los montes submarinos controlan la morfoestructura y arquitectura local del margen y causan modificaciones, de diversa escala, de las condiciones oceanográficas (Fig. 2). Altos morfológicos como la Dorsal de
Alborán compartimentan la fisiografía de la cuenca y otros como el Banco de Gorringe o el Monte submarino de Tore, separan las actuales cuencas abisales atlánticas al oeste de Iberia. Cabe señalar el papel ejercido
por el Banco de Guadalquivir que obstaculizó el avance de la unidad Alóctona del Golfo de Cádiz, emplazada durante el Tortoniense, y el Banco Le Danois que ha favorecido la formación y el desarrollo de subsidencia en la cuenca intratalud Asturiana. La configuración reciente de los montes submarinos también ha sido
remodelada por los procesos sedimentarios que les afectan y se agrupan en cuatro tipos en base al mecanismo de transporte de sedimento: i) los procesos pendiente abajo de los montes (flujos en masa, flujos turbidíticos, y deslizamientos) dominan en la Dorsal de Alborán y en los bancos de Gorringe, de Portimao y de
Galicia aunque aparecen en mayor o menor medida en todos los montes; ii) los procesos que actúan paralelos a los montes (corrientes contorníticas) dominan en los bancos de Djibouti, de Guadalquivir, de Galicia y
Le Danois. La acción de estas corrientes, junto con los cambios del nivel del mar, esculpen niveles de terrazas en la cumbre de los montes submarinos más someros y forman plataformas aisladas (v.g. Dorsal de
Alborán, Monte submarino de Emile Baudot); y iii) los procesos mixtos.
Conclusiones: recopilación de los montes submarinos de Iberia
Se presenta una recopilación de 15 montes submarinos en el entorno de los márgenes continentales de Iberia
y del dominio oceánico Atlántico que representan bien la geodiversidad de estos rasgos morfológicos. Se clasifican estos montes en dos grupos en base a su origen: i) los originados por estructuras de primer orden
(tectónicas o volcánicas) que incluyen los montes de grandes dimensiones (longitudes superiores a 50 km) y
linealidad, representados por la Dorsal de Alborán y la mayor parte de los montes submarinos de los márgenes y dominios oceánicos atlánticos); y ii) los originados por altos de basamento y elevaciones magmáticas más puntuales, con dimensiones menores (longitudes inferiores a 20 km), que aparecen en forma solitaria o formando alineaciones de montes, representados por el resto de los montes submarinos estudiados en
los dominios mediterráneos. Aunque el origen de los montes submarinos estudiados es diverso (elevaciones
de basamento asociadas a fallas extensionales, cabalgamientos, volcanismo y diapirismo), existe una importante reactivación posterior de tipo tectónica que ha tenido lugar a lo largo del Oligoceno-Mioceno (bancos
Le Danois y de Galicia), del Plioceno (bancos de Gorringe y Portimao), e incluso del Cuaternario (Dorsal de
Alborán). La presencia de los montes submarinos en el entorno de los márgenes de Iberia ha favorecido,
tanto en el pasado como en el presente, el desarrollo de procesos relacionados con inestabilidades sedimentarias y flujos en masa, corrientes de fondo y procesos de construcciones biogénicas como son los arrecifes de corales de aguas frías y acumulaciones de fondos de “maërl” en plataformas carbonatadas sobre los
montes más someros.
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Introduction and state of the art
Seamounts (Smt.) are morphological sea-floor features characterised as isolated mountains, or chains
of successive highs with reliefs of at least 1,000 m
(Kennet,
1980;
International
Hydrographic
Organization, 2008) but today there is a trend towards
using this term for reliefs of heights up to 100 m
(Staudigel et al., 2010; Staudigel and Clague, 2010;
Würtz et al., 2014); researchers recognise smaller
seamounts as being from 50-100 m (Smith and Cann,
1990; Wessel et al., 2010), and nowadays,
Mediterranean seamounts are being catalogued
according to this criteria (Würtz et al., 2014). In a general sense, any smaller mounts that rise up to 100 m
from the seafloor, the so called hills or knolls, may be
also considered seamounts, however, when these
occur on continental margins they are usually
referred to as banks. Their origins are varied. They
can be formed by tectonic structures (faults and
folds), caused by diapiric movements, mud volcanism and biostromes, although the majority correspond to magmatic constructions, especially in the
oceanic crust domain. On continental margins, the
major seamounts, sensu strictu, have been observed
for example, on the Atlantic margin of the Iberian
Peninsula (Galicia Bank; Ercilla et al., 2011), the
Cantabrian margin (Le Danois Bank; Ercilla et al.,
2008a), the northern margin of the British Isles
(Hatton Bank; Hitchen, 2004), and the eastern margin
of North America (Flemish Cap Bank; Piper, 2005).
Historically, since seafarers began to encounter
seamounts centuries ago, they have captured the
curiosity of researchers from many disciplines, for
instance Charles Darwin was the first person to
describe the processes of guyot formation in oceanic
domains (Menard, 1984). However, the detailed
exploration of seamounts has only been possible
over the past few decades thanks to technological
advances. The development of swath bathymetry in
the 1990s caused an explosion in deep sea exploration that allowed the discovery and mapping of
many seamounts. The application of bathymetric
techniques using satellite altimetry enabled us to
build up a picture of seamount distribution in the
oceans (Smith and Sandwell, 1997). The characterisation and distribution of seamounts have led to a better understanding of the deep ocean, seafloor
spreading, and plate tectonics. Subsequently, numerous geological, physical and biological characteristics
of seamounts have been described, including their
important role in global oceanic circulation and the
biogeography of the deep seas (Turnewitsch et al.,
2013). A significant increase in seamount research
resulted from the United Nations General Assembly
mandate on sustainable fishing, which was implemented from 2004 to 2009. The mandate urged fishing nations and Regional Fisheries Management
Organisations to identify and protect vulnerable
marine ecosystems, as well as assess the impact of
deep-sea fishing in the high seas beyond national
jurisdictions (Durán Muñoz et al., 2012). This came in
response to the global expansion of commercial
deep-sea fishing in the mid-1950s, when seamounts
became the focus of intensive commercial exploitation. Despite more than 100 years of study, many
questions remain unanswered.
The relatively small dimensions of seamounts
make them excellent subjects for geological study;
they represent reference zones for analysing marine
geological processes on a larger scale. Seamounts
control surrounding geo-environmental processes
and interfere with water-mass dynamics, producing
upwelling currents and improving nutrient availability. Furthermore, they have a high biological productivity related to the development of interesting habitats and dynamic changes with respect to the
adjacent margins. They are little influenced by continental sources and this makes them key in palaeooceanographic and palaeo-climatalogical studies. In
addition, they can be natural laboratories for studying
marine “source-to-sink” relationships as they present
all the elements of this chain: source area, sediment
transference systems and final deposition, as well as
re-sedimentation systems. Seamounts provide an
integrated and interesting view of the majority of
marine sedimentary systems, including sedimentary
instability, pelagic, hemipelagic, turbiditic and contouritic systems. Tectonic reactivation can modify the
original structures, either by increasing their elevation or favouring their break-up, and this provides
information on local and regional deformation
regimes. Lastly, seamounts favour the local and
regional pattern of subsurface fluid migration, influencing the development of sedimentary instabilities
and/or specific habitats.
Since the 1970s, the Iberian seamounts (e.g., the
Gorringe Bank and Tore Seamount) have been surveyed using seismic reflection profiling, as well as
other techniques (magnetic anomalies, bathymetry,
dredging and gravity profiles). However, there was no
detailed knowledge of these seamounts until the
improvement in data acquisition techniques in the
90s, particularly multibeam bathymetric data. Historic
and recent bathymetric surveys from Spanish national projects (e.g., TASYO, PRESTIGE, ERGAP, CONTOURIBER, SAGAS bis and MONTERA), international
research projects (MVSEIS, MOUNDFORCE, SWIM,
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WESTMED, SEAMOUNT, OASIS, HERMES, SIMoN),
Economic Exclusive Zone and Outer Continental
Shelf Delimitation projects from Spain and Portugal,
and the Spanish national plan for fisheries, have contributed to our knowledge of the morphostructure of
seamounts
and
their
sedimentary
record.
Geophysical studies are enabling us to gain more
detailed information on the structural evolution of the
Iberian margins. In addition, characterising the sediment types on seamount tops and walls allows us to
understand the sedimentary processes of the Iberian
deep sea areas.
Several authors have looked at particular
seamounts, including noteworthy contributions by
Acosta et al. (2001a) and Acosta et al. (2003) on the
seamounts of the Balearic Promontory; Palomino et
al (2011) who studied the role of the Djibouti Banks
within the basin’s general morphosedimentary
scheme; Ferranti et al. (2014) made a detailed morphostructural analysis of the Gorringe Bank; and
Ercilla et al. (2008b) and Ercilla et al. (2011) focused
on the Le Danois and Galicia banks, providing a current view of their sedimentary processes. Recently,
Maestro et al. (2013) have presented a complete
review of the geomorphology of the continental margins of Iberia which also address general aspects of
many seamounts considered in this work.
Seamounts are widespread across all the Iberian
margins and adjacent oceanic domains (Figs. 1 and
2). Their characteristics and origins are different and
they represent a complete catalogue of the global
geodiversity characterising these features. Current
scientific knowledge of seamounts is relatively moderate; there is a lack of systematic geological studies
on the Iberian examples, with the exception of the
surveys carried out as part of the Portuguese and
Spanish Exclusive Economic Zone programs.
Seamount research is at the beginning of a steep
data-collection curve.
The main aim of this paper is to present, for the
first time, an overview of the seamounts in the Iberian
region; their occurrence, size and distribution are presented as well as the associated geological processes. This paper offers a broad perspective of the geological research on the seamounts around Iberia. A
total of 15 selected seamounts have been analysed
and these have been assigned the numbers that
appear in Figure 1: the Ses Olives (6), Ausiàs March
(7) and Emile Baudot (8) seamounts from the Balearic
Promontory; the Northern Alboran Ridge (13), and the
Djibouti Banks (comprising the Avempace -14.1,
Herradura -14.2, Herradura Spur -14.3 and Djibouti
Ville -14.4 seamounts) in the Alboran Sea; the
Guadalquivir Bank (27), Portimao Bank (28), Gorringe
Bank (31) and Coral Patch Seamount (29) from the
Gulf of Cadiz and adjacent Atlantic oceanic domains;
the Tore Seamount (33) in front of the Portuguese
margin; the Galician Bank (36) from northwest Iberia,
and the Le Danois Bank (40) from the Cantabrian margin (Fig. 1 and Table 1). In this regard, it is noteworthy
that we have used new, unpublished data on the Gulf
of Cadiz and the Alboran Sea seamounts, which were
obtained through the project MONTERA.
Geological setting
The margins and adjacent oceanic basins around the
Iberian Peninsula are differentiated into two welldefined geodynamic domains: the Mediterranean
margins developed in the context of the Alpine
Orogeny from the Upper Oligocene onwards, and the
Atlantic domain whose margins formed by rifting
from the Late Triassic to the Upper Cretaceous. The
most recent morphogenetic episode of most of these
seamounts, even the Atlantic ones, may be linked to
their evolution during the Alpine orogeny, which
greatly influenced the Iberian margins from the
Eocene to Miocene, and right up to the present day
(Fig. 1). This is due to the successive compressive
deformation affecting the Iberian Peninsula, both
northwards (the Pyrenean orogen) and southwards
(the Betic-Rif orogen) (De Vicente and Vegas, 2009).
Since the Upper Tortonian, the Iberian Peninsula has
been located just north of the present-day boundary
between the African and Eurasian plates (Srivastava
et al., 1990). Recent geodynamic models shows the
existence of a NW-SE to WNW-ESE oblique convergence at a rate of about 4 mm/yr between these
plates (e.g., Nocquet and Calais, 2004; Stich et al.,
2006). This plate boundary extends from the western
Azores triple junction through the Gloria Fault, located westwards of the Gorringe Bank, and continues
eastwards into the Gulf of Cadiz along the SWIM fault
zone as suggested by recent models (Zitellini et al.,
2009). This fault zone connects with the Rift-Tell
System on the southern boundary of the
Mediterranean Orogenic Belt (Mauffret et al., 2007;
Terrinha et al., 2009; Zitellini et al., 2009; Cunha et al.,
2012; Rosas et al., 2012) (Fig. 1). Recently it has been
proposed that in the south-western Iberia margin a
new subduction zone of the Atlantic oceanic crust
beneath Iberia may be forming, resolved with northwestern verging thrusts of the Gorringe Bank and the
Horseshoe Abyssal Plain and connected by the SWIM
fault zone to the Betic-Rif orogen (Duarte et al., 2013).
In the Mediterranean domain, seamounts have
been identified in the Balearic Promontory and the
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Figure 1. Location of the main seamounts (Smt.,) along the Iberian margins: 1- Soller Smt., 2-Morrot de Sa Dragora Smt., 3- MS1-S or
Stony Sponge Smt., 4-MS-2 or Xabia Smt., 5-Cabo de la Nao Smt, 6-Ausiàs March Smt., 7-Ses Olives Smt., 8-Emilie Baudot Smt., 9-MS3 or Bel Guyot, 10-Jaume I Smt., 11-MS-4 or Vallseca Smt., 12- Colom Smt., 47- Seco de Palos Bank, 48-Cresques Smt. (NE Iberia); 13Northern Alboran Ridge, 14-Banks of Djibouti, 15-Xauen Bank, 16-Tofiño Bank, 17-Ibn Batouta Smt., 18-Chella or Seco de los Olivos Bank,
19-Pollux Bank, 20-Adra Ridge, 21-Maimonides Ridge, 22-Al Mansour Ridge, 23-Yusuf Ridge, 24-Les Cabliéres Bank, 25-Provençaux, Bank
26-Tres Forcas Promontory, 49-Abubacer Ridge (SE-Iberia); 27-Guadalquivir Bank, 28-Portimao Bank, 50- Cadiz Diapiric Ridge, 51Guadalquivir Diapiric Ridge (SW-Iberia); 29-Coral Patch Smt., 52-Coral Patch Ridge, 30-Ampere Smt., 31-Gorringe Bank, 32-Hirondelle
Smt., 33-Tore Smt. (W-Iberian); 34-Porto Smt., 35-Vigo Smt., 36-Galicia Bank, 37-La Coruña Smt., 38-Finesterre Smt. (Galician or NWIberian); 39-Vizco High, 40-Le Danois Bank, 41-Ecomarge High, 42-Santander Promontory, 43-Landes Smt., 44- Jovellanos Smt., 45Charcot seamounts, 46- Vizcaya Smt., (Cantabrian or N-Iberian). BP: Balearic Promontory; Mn: Menorca Island; M: Mallorca island; I: Ibiza
island; VT: Valencia Trough; SBAB: South Balear-Algerian Basin; EB: Emile Baudot Escarpment; AB: Alboran Basin; YF: Yusuf Fault; AF: Al
Idrissi Fault; GCCM: Gulf of Cadiz continental margin; SPM: South-Portuguese Margin; AS: Seine Abyssal Plain; SF: SWIM Fault Zone; AH:
Horseshoe Abyssal Plain; AT: Tajo Abyssal Plain; PCM: West-Iberian or Portugal continental margin; AI: Iberia Abyssal Plain: GCM: northwest-Iberian or Galician continental margin; AB: Gulf of Biscay Abyssal Plain; CCM: north-Iberian or Cantabrian Continental Margin; AMP:
Asturian Marginal Plateau.
Figura 1. Localización de los principales montes submarinos (MS) en los distintos márgenes de Iberia: 1-MS Soller, 2-MS Morrot de Sa
Dragora, 3-MS1-S o MS Stony Sponge; 4-MS-2 o MS Xabia, 5-MS Cabo de la Nao, 6-MS Ausiàs March, 7-MS Ses Olives, 8-MS Emilie
Baudot, 9-MS-3 o Guyot Bel, 10-MS Jaume I; 11-MS-4 o MS Vallseca; 12-MS Colom, 47-Seco de Palos Bank, 48-MS Cresques (NE Iberia);
13-Dorsal de Alborán Norte, 14-Bancos de Djibouti, 15-Banco de Xauen, 16-Banco de Tofiño, 17-MS Ibn Batouta, 18-Banco de Chella o Seco
de los Olivos, 19-Banco de Pollux, 20-Dorsal de Adra, 21-Dorsal de Maimonides, 22-Dorsal de Al Mansour, 23-Dorsal de Yusuf, 24-Banco
de Les Cabliéres, 25-Banco Provençaux, 26-Promontorio Tres Forcas, 49-Dorsal de Abubacer (SE-Iberia); 27-Banco del Guadalquivir, 28Banco de Portimao, 50-Dorsal Diapírica de Cádiz, 51-Dorsal Diapírica del Guadalquivir (SO-Iberia); 29-MS Coral Patch, 52-Dorsal de Coral
Patch, 30-MS Ampere, 31-Banco de Gorringe, 32-MS Hirondelle, 33-MS Tore (O de Iberia); 34-MS Porto, 35-MS Vigo, 36-Banco de Galicia,
37-MS La Coruña, 38-MS Finesterre (Margen de Galicia o del Noroeste de Iberia); 39-Alto Vizco, 40-Banco de Le Danois, 41-Alto Ecomarge,
42-Promontorio de Santander, 43-MS Lande, 44-MS Jovellanos (N-Iberia), 45-Montes submarinos de Charcot, 46-MS Vizcaya (Margen
Cantábrico o del Norte de Iberia). Otros rasgos geográficos y geológicos mencionados en el texto: BP: Promontorio Balear; Mn: Isla de
Menorca; M: Isla de Mallorca; I: Isla de Ibiza; VT: Cuenca de Valencia; SBAB: Cuenca Algero-Balear; EB: Escarpe de Emile Baudot; AB:
Cuenca de Alborán; YF: Falla de Yusuf; AF: Falla de Al Idrissi; GCCM: Margen continental del Golfo de Cádiz; SPM: Margen Surportugués;
AS: Llanura Abisal de Sena; SF: Zona de falla SWIM; AH: Llanura Abisal de La Herradura; AT: Llanura Abisal de Tajo; PCM: Margen continental de Portugal o del Oeste de Iberia; AI: Llanura Abisal de Iberia; GCM: Margen continental de Galicia o del Noroeste de Iberia; AB:
Llanura Abisal del Golfo de Vizcaya; CCM: Margen continental Cantábrico o del Norte de Iberia; AMP: Plataforma Marginal de Asturias.
488
Figure 2. Main water masses around Iberia cited in the text. Taken from Hernández-Molina et al., (2011).
Figura 2. Principales masas de agua alrededor de Iberia tal como se citan en el texto. Tomado de Hernández-Molina et al., (2011).
Alboran Sea Basin (Fig. 1). Both areas formed in the
context of the western Mediterranean back-arc Upper
Oligocene-Miocene rifting (Jolivet and Faccena,
2000), which resulted from the splitting of a previous
Eocene Alpine Belt (Carminati et al., 2012). The
Balearic Promontory is 350 km long, 105 km wide and
its flanks are approximately 2,000 m high. The
promontory is flanked on its south-eastern side by the
NE-SW oriented Emile Baudot Escarpment that separates it from the south Balearic-Algerian Basin to the
southeast (Acosta et al., 2003). The promontory is a
large terrestrial and submarine elevation in the western Mediterranean Basin which corresponds to a continental block located in the north-eastern prolongation of the External Betic Belt (Rehault et al., 1985). Its
northern boundary has thrust faults that principally
verge in the Valencia Trough, and the southern
boundary is dissected by NE-SW normal faults rela-
ted to oceanic spreading in the western
Mediterranean (Vegas, 1992a; Acosta et al., 2001a).
The Alboran Sea Basin was formed inside the
Gibraltar Arc (Betics-Rif orogen) during the Late
Oligocene and Miocene (Platt et al., 2003), and it has
been under compression from the Late Miocene to
the present (Martínez-García et al., 2013). Stretching
and normal faulting in the extensional phase produced thinning of the continental crust accompanied
by several andesitic volcanic episodes (Duggen et al.,
2004; Gill et al., 2004).
In the Atlantic domain, seamounts have been identified in several geological domains: the Gulf of Cadiz,
especially in its northern part (South Portuguese
Margin), and the adjacent Atlantic realm, western
Iberia (Portugal), north-western Iberia (Galician) and
the northern Iberian margins (Cantabrian) (Fig. 1).
The southern Portuguese margin began to be
489
Id.
N°
Location
Seamount
Name
Latitude
Longitude
Max/Min.
water
depth (m)
Lenght/
Width
(km)
Height
(m)
Area
(km2)
Max/Min.
slope (°)
6
NE Iberia
Balearic
Promontory
Ses Olives
Smt
38°58 N
02°02 E
995/250
11.5/6.4
775
59
40.2/0.3
7
NE Iberia
Balearic
Promontory
Ausiàs March
Smt
38°44 N
01°49 E
583/86
13.2/5.9
497
73
32.3/0.1
8
NE Iberia
Balearic
Promontory
Emile Baudot
Smt
38°44 N
02°29 E
702/80
15.2/7.6
620
98
31.7/0.0
13
SE Iberia
Alboran Sea
North
Alboran
Ridge
35°53.33’N
03°02’W
1,600/+16
105/22
1,600
2,100
57/0.2
14
SE Iberia
Alboran Sea
Banks of
Djibouti
14.1 SE Iberia
Alboran Sea
Avempace
Smt
36°22`N
03°58°`W
970/250
12.5/10
700
83
53.3/0.01
14.2 SE Iberia
Alboran Sea
Herradura
Smt
36°12`N
03°45`W
930/270
17.8/16
660
202
52/0.02
14.3 SE Iberia
Alboran Sea
Herradura
Spur Smt
36°18.56’N
03°41.96’W
867/436
6.1/4.9
431
22.5
22.8/0.8
14.4 SE Iberia
Alboran Sea
Djibouti Ville
Smt
36°08`N
03°33’W
870/200
10.5/9.7
670
77
43.5/0.02
27
SW Iberia
Gulf of Cadiz
Margin
Guadalquivir
Bank
36°22.89`N
7°46.33`W
670-1115
11.15/0.275
395-840
82
40/3
28
SW Iberia
Gulf of Cadiz
Margin
Portimao
Bank
36°12.55 N
8°39.34’W
3,8003,200
93/18-25
400-900
1,800
12/0.01
29
SW Iberia
Portuguese
Margin
Coral Pacth
Smt
34°56.100 N
11°52.917’W
5,000-560
120/70
400
8,400
20/3
31
SW Iberia
Portuguese
Margin
Gorringe
Bank
36°38.750 N
11°18.417’W
4,800/20
200/70
4,700
14,000
30/5
33
W Iberia
Portuguese
Margin
Tore Smt
39°23.567’N
12°53.867’W
5,200/
2,300
239/130
2,900
31,000
11/3
36
NW Iberia
Galicia
Margin
Galicia Bank
42°41,73’N
11°45,16’W
4,100/605
84/60
3,000
2,946
49/0.15
40
W Iberia
Cantabric
Margin
Le Danois
Bank
44° 4.78’ N
4° 47.07’ W
4,400 /510
72 / 15
3,900
1,150
20/0.1
Table 1. Summary of the location, geometric parameters (depth, length, width, height, area, and slope gradient) that characterise the 15
studied Iberian seamounts (Smt). Length and width are measured as the longest and shortest axes, and heights from the shallowest part
of each seamount to the adjacent seabed.
Tabla 1. Resumen de la localización y parámetros geométricos (profundidad, longitud, anchura, altura, área, y pendiente) que caracterizan los 15 montes submarinos de Iberia estudiados. La longitud y la anchura se miden como los ejes de mayor y menor longitud respectivamente, y la altura desde la parte más superficial de cada monte hasta la profundidad del fondo marino adyacente.
formed during Triassic-Late Cretaceous rifting phases
related to the opening of the Neo-Tethys and Central
Atlantic Ocean (Terrinha, 1998). The initial formation
of this margin took place during the early stages of
the opening of the central Atlantic (Late TriassicMiddle Jurassic) in a transtensional continental shear
zone which evolved into a rifted transform margin
during the Cretaceous (Vegas et al., 2004). The general extensional regime was punctuated by short-lived
compressional periods during the Jurassic and near
the boundary Jurassic-Cretaceous. From the end of
Late Cretaceous and through Late Miocene, the
southern Portuguese margin suffered multiphased
tectonic inversion, controlled mainly by the N-S convergence between the Eurasian and African plates
and the formation of the Betic-Rif orogenic arc in the
Gulf of Cadiz (Maldonado et al., 1999; Rosenbaum et
al., 2002; Terrinha et al., 2009).
The formation of the western Iberian margin is
related to the multiphased rifting that separated the
the western Iberian and Newfoundland conjugate
margins, from the Late Triassic to Early Cretaceous,
490
leading to the opening of the North Atlantic Ocean.
Both margins have been highlighted as classic examples of poor magma rifted margins (Sibuet et al.,
1979; Boillot et al., 1995; Pinheiro et al., 1996; PéronPinvidic et al., 2007; Reston et al., 2007; PéronPinvidic et al., 2007; Tucholke et al., 2007; PéronPinvidic and Manatschal, 2009). The first rifting phase
occurred from the Late Triassic into early Jurassic,
characterized by extension without continental separation. The second phase occurred from the Late
Jurassic through the Early Cretaceous and had three
episodes (Whitmarsh et al., 2001; Sibuet et al., 2007;
Tucholke et al., 2007): 1- rifting and continental crust
breakup in the southern part of the rift (Late JurassicBerriasian); 2- rifting and continental crust breakup in
the northern part of the rift and rifting of sub-continental mantle lithosphere in the southern part
(Valanginian-Hauterivian); 3- rifting and exhumation
of the continental lithosphere mantle (BarremianAptian), forming the zone of exhumed continental
mantle (ZECM). According to a recent work by
Sallarés et al. (2013), the serpentinized peridotites
found in the basement of Gorringe Bank may be part
of an older ZECM, recording the northwards migration of the rifting. Thus, the rifting and later the
oceanic spreading progressively migrated from the
Gorringe Bank area northwards, reaching the northwestern Iberian margin at about 112 Ma (Pinheiro et
al., 1996). Moreover, the Gorringe Bank has been a
geodinamic key point since Mesozoic times, due to its
location between the domains of the western Iberian
and southern Portuguese margins and currently near
to the Eurasian (Iberia)-African (Nubia) plate boundary (Jiménez-Munt et al., 2010).
Since the Late Cretaceous the western Iberia margin has been affected by several episodes of alkaline
magmatism, which extended from the Tore seamount
(~104-80Ma) through the Tore-Madeira Rise and
reached the Madeira Islands (~5 Ma) located in the
central Atlantic Ocean (Geldmacher et al., 2006; Merle
et al., 2006). Several alkaline magmatic episodes have
also been recognized onshore, for instance, at
Monchique (~72 Ma) located in the south-west mainland of Portugal and offshore in the Ormonde Smt.
(~66-60 Ma) on the Gorringe Bank, the Coral Patch
seamount (32 Ma) and the Ampere Smt. (31 Ma)
(Merle et al., 2009; Geldmacher et al., 2011). This
magmatic activity has been interpreted as the trace of
the Madeira hotspot (e.g., Geldmacher et al., 2011).
Several compressional episodes associated with
changes in the convergence direction between the
African and Eurasian plates, since the Eocene until
the Present, have been accommodated by thrusting
along major structures. This is the case for the north-
westwards thrusting of the Gorringe Bank over the
Tagus Abyssal Plain (Terrinha et al., 2003), and of the
Coral Patch Smt. in the same direction over the
Horseshoe Abyssal Plain (Hayward et al., 1999;
Martínez-Loriente et al., 2013; Martínez-Loriente et al.,
2014).
The north-western Iberian (Galician) margin
formed near the triple junction between North
America, Iberia and Eurasia in the Upper Cretaceous
from magnetic anomalies MO to C33o (118 to 80 Ma),
which allowed the oceanic opening in the Bay of
Biscay (Sibuet and Collette, 1991; Sibuet et al., 2004).
Finally, the northern Iberian (Cantabrian) margin, the
youngest Atlantic margin in Iberia, was formed in the
Upper Cretaceous and Palaeogene during the early
opening of the Bay of Biscay (Le Pichon et al., 1971;
Sibuet et al., 2004). Offshore, the Pyrenean orogeny
(Late Cretaceous to Eocene) caused the partial closure of the Bay of Biscay and the uplift of the margins
by thrusting (Gallastegui et al., 2002), simultaneously,
in part, with seafloor spreading in the basin (Sibuet et
al., 2004). These processes migrated westwards, also
inverting the north-western Iberian margin in the
Lower Miocene (Alvarez-Marrón et al., 1997; Sibuet et
al., 2007; Vázquez et al., 2008a).
Methods
This paper is based on the study of combined data
obtained by means of multibeam echo sounders
(Kongsberg-Simrad EM-12S, EM-120, EM300,
EM1000 and ATLAS Hydrosweep DS), ultra-high
(parametric TOPAS PS 018 echo sounder and ATLAS
Parasound P-35) and high reflection seismic systems
(EG&G sparker and 3-channel Airgun). The data has
been compiled from several oceanographic expeditions sponsored by Spanish projects (TASYO,
MOUNDFORCE, PRESTIGE, ERGAP, SAGAS bis, CONTOURIBER, MONTERA) and Portuguese national programmes developed on the Iberian margins by various governmental organisations. In particular,
complete multibeam coverage of the floor of the
Balearic Sea and the Galicia Margin was recorded
during the Spanish Exclusive Economic Zone surveys
(IEO-IHM-ROA, 1999; Gómez-Ballesteros, 2000).
The morphography of the seamounts has been
systematically analysed using the geographic information system ArcGis software. This considers location and a series of geometric parameters (depth,
length and width, height, area, and slope gradient)
where the lengths and widths are the longest and
shortest axes respectively of these features in the
bathymetric cartography, and relief is the measure of
491
height from the adjacent seafloor to the summit of the
seamount. Table 1 summarises this characterisation.
Seamounts in the Balearic Promontory
Morphology
Fourteen seamounts (Soller, Morrot de Sa Dragora,
MS1-S or Stony Sponge, MS-2 or Xabia, Cabo de la
Nao, Ausiàs March Smt., Ses Olives, Emilie Baudot,
MS-3 or Bel Guyot, Jaume I, MS-4 or Vallseca, Colom,
Cresques seamounts, Seco de Palos Bank) have been
recognised in the Balearic Promontory and Valencia
Trough (numbers 1 to 12, 47 and 48 in Fig. 1). In this
section, three selected seamounts (numbers 6, 7 and
8 in Fig. 1), which are under consideration as
“Protected Marine Areas” of Spain, are described.
These are: the Ses Olives (6) (also known as Monte
Norte) (Fig. 3A), Ausiàs March (7) (also called Monte
Sur) (Fig. 3B) and Emile Baudot (8) seamounts (Fig.
3C). They are located to the east of the islands of Ibiza
and Formentera on the Balearic Promontory (Fig. 1).
The Ses Olives Smt. (summit at 250 m water
depth) is approximately NE-SW trending, rectangular
in shape, and occupies an area of 50 km2 (11.5 km
long and 6.4 km wide) (Table 1). The top of the
seamount is flat (< 2°) and displays three small elevations (< 30 m high). Its flanks slope up to 40°. The
main morphological features identified on this
seamount are: a slide scar, slumps, and pockmarks
(Fig. 3A). An amphitheatre-like scar is observed on
the south-western flank where deposits have been
eroded and transported south-westwards. Slump
deposits occur on the south-eastern flank where NESW faults are found bounding this seamount. An
extensive pockmark field has been identified on the
western and southern flanks. The pockmarks are circular (150 to 500 m in diameter; 10 to 35 m in relief),
giving the seafloor an “orange peel” texture, and
tend to group into chains following the main tectonic
trend (Fig. 3A) (Gómez-Ballesteros, 2000; Acosta et
al., 2001b).
The Ausiàs March Smt. (summit at 86 m water
depth) is approximately NE-SW trending, has an elongated shape, and occupies an area of about 73 km2
(13.2 km long and 5.9 km wide) (Table 1). The planar
top of this structure has moderate slope gradients (2°
to 4°). The main morphological features identified on
this seamount are: fault scarps, scars, slumps,
mounds, and pockmarks (Fig. 3B). The most striking
feature is a NE-SW fault with a topographic expression of more than 25 m dissecting the top (GómezBallesteros, 2000; Acosta et al., 2001b). Slide scar and
slump deposits occur on the north-eastern flank.
Elongated circular mounds forming chains aligned
with the NE-SW fault are recognised in the northern
sector. The pockmark field occurs in the north-eastern
sector of the seamount (Fig. 3B), individual pockmarks ranging 150-500m in diameter and have 10-35
reliefs, and tend to group into chains aligned to NESW faults.
The Emile Baudot Smt. (summit at 80 m water
depth) is approximately NE-SW trending, has an elongated shape and occupies an area of about 98 km2
(15.2 km long and 7.6 km wide) (Table 1). The top is
planar (0-2°) and the flanks have important slope gradients (up to 31°) (Acosta et al., 2001a). The main
morphological features identified on this seamount
are: erosional surfaces, biogenic patches, gullies,
slumps, scars and volcanic intrusions. Erosional surfaces, as well as biogenic patches formed by accumulations of coralline algae (maërl) and carbonate
clasts (rodoliths) are recognised on the top (Acosta et
al., 2003). A network of NW-SE orientated gullies and
slide scars have been identified on the upper sector of
the flanks (Gómez-Ballesteros, 2000; Acosta et al.,
2001a), and slumped and blocky sediments are present at their bases. A volcanic field (513 km2) has also
been mapped on the flanks (Gómez-Ballesteros, 2000;
Acosta et al., 2001a; Acosta et al., 2004) (Fig. 3B). This
comprises 118 pointed and flat-topped, cone-shaped
pinnacles from 8 to 501 m in height and 141 to 1741
m in diameter (Acosta et al., 2001a,b) (Fig. 3 C, D).
Genetic processes
The Ses Olives and Ausiàs March seamounts are
structural highs which are caused by the conjugate
fault system oriented NE-SW and NW-SE (GómezBallesteros, 2000; Acosta el at., 2001a). The Emile
Baudot Smt. is a NE–SW elongated guyot formed by
the south-west prolongation of the southern mountain ranges of Mallorca Island, probably intruded by
volcanics (Acosta et al., 2001a), as indicated by geomagnetic data (Palomo et al., 1974; IEO-IHM-ROA,
1999). Some of the differentiated pinnacles around
this seamount are almost perfectly conical in shape;
these are Middle Miocene-Recent and intrusive in
nature (Martí et al., 1992; Gómez-Ballesteros, 2000;
Acosta et al., 2003). An olivine basalt sample taken on
the top of this seamount has led to a similar origin
being ascribed to the other volcanic features (Acosta
et al., 2004). The southern limit is marked by the
Emile Baudot Escarpment, a NE-SW linear scarp that
suffered extensive erosion in the Messinian (Rehault
et al., 1985; Acosta et al., 2001a).
492
Figure 3. The Balearic Promontory seamounts (NE-Iberian): hill-shade and geomorphological maps of (A) the Ses Olives (B) the Ausiàs
March and (C) the Emile Baudot Seamount and (D) selected single channel seismic of the Emile Baudot Smt. Profile location in C. Legend:
Pl-Q, Plio-Quaternary deposits. Modified from Gómez-Ballesteros (2000).
Figura 3. Montes submarinos del Promontorio Balear (NE-Iberia): Mapas de Sombras y Geomorfológicos de los Montes submarinos de
(A) Ses Olives, (B) Ausiàs March y (C) Emile Baudot; y (D) Perfil de sísmica monocanal a través del Monte Submarino de Emile Baudot.
Localización del perfil en C. Leyenda: Pl-Q, Depósitos Plio-Cuaternarios. Modificada de Gómez-Ballesteros (2000).
Recent geological processes
The main geological processes affecting the three
Balearic seamounts studied are sedimentary instability, volcanism, seepage, and carbonate formation
(Fig. 3). Numerous areas of instability related to tectonics, erosion at head scarps and sediment remobilisation by slumps and slides have been identified
(Gómez-Ballesteros, 2000: Acosta et al., 2001a,b).
Middle Miocene-Recent volcanic activity has been
located close to the Emile Baudot Escarpment (Martí
et al., 1992) and associated extensional tectonics is
evidenced by a folded sequence on south-western
flank of the Emile Baudot Smt. Evidence of seepage
(gas/water) is characterised by pockmark depressions
and this may be due to a subsurface gas/water pres-
493
sure factor that favours, if not triggers, the sediment
failures (Acosta et al., 2003). The recent volcanic
structures present in the region suggest that most of
the pockmarks observed may have formed due to the
migration of gas and associated water from a residual
sub-bottom hydrothermal field, via neo-tectonic
faults (Acosta et al., 2001b). Most water masses in the
basin interact with the surface of the seamounts (Fig.
2). In particular, the shallow-water mass, the Modified
Atlantic Water (MAW), interacts with the shelf and
upper slope and results in the formation of coralline
algae accumulations (maërl) on the top of the
seamounts. These are made up of round, centimetresized carbonate clasts (rodoliths) which carpet the
seafloor (Acosta et al., 2003).
Seamounts in the Alboran Sea
Morphology
Fifteen major seamounts (Northern Alboran Ridge,
Djibouti Banks, Xauen Bank, Tofiño Bank, Ibn Batouta
Smt., Chella or Seco de los Olivos Bank, Pollux
Seamount, Adra Ridge, Maimonides Ridge, Abubacer
Ridge, Al Mansour Ridge, Yusuf Ridge, Les Cabliéres
Bank, Provençaux Bank, and Tres Forcas Promontory)
have been recognised in the Alboran Sea (numbers
13 to 26 and 49 in Fig. 1). Two selected areas are
described here: the Northern Alboran Ridge (number
13 in Fig. 1 and Table 1) and the Djibouti Banks (numbers 14.1 to 14.4 in Fig. 1 and Table 1), because of
their oceanographic and geological location in the
central part of the basin (Figs. 4 and 5). The northern
Alboran Ridge (NAR) is the north-eastern segment of
the Alboran Ridge chain which follows an ENE-WSW
trend (Figs. 1 and 4) between the Yusuf Fault escarpments to the northeast and the Xauen Bank to the
southwest (Fig. 1). It is bounded to the north by the
Alboran Trough and the Western Alboran Basin, to
the south by the Southern Alboran Basin and to the
west by the Al Idrisi Fault. The Djibouti Banks are
located on the Djibouti-Motril Marginal Plateau
(Palomino et al., 2011), on the northern margin of the
Alboran Basin, where four major seamounts have
been recognised forming a NW-SE trending chain at
the south-western boundary of this marginal plateau:
Avempace Bank (14.1), Herradura Bank (14.2),
Herradura Spur (14.3) and Djibouti Ville Bank (14.4)
(500 m on the north-eastern flanks to 1,000 m on the
south-western flanks) (Fig. 5A).
The NAR can be divided into three sectors based
on the differences in the water depth of its summits
(Fig. 4): the shallowest (summit at 0-115 m water
depth) is in the north-eastern sector, and is trape-
zoidal in shape (75 km length, 22 km width); the intermediate (summit at 83-115 m water depth) is in the
central sector and has a strongly linear crest (32 km
long and 23 km wide); and the deepest (summit at
257-400 m water depth) is in the south-western sector
and has a smooth crest (28 km long and 20 km wide).
The NAR occupies an area of around 21,000 km2. The
top of the NAR is relatively flat (<2°) but locally reaches up to 5°; the lowest gradients occur in the northeastern and central sectors which are configured as
isolated shelves (Bárcenas et al., 2001). The small
Alboran Island (642 m long, 265 m maximum wide
and 15 m maximum height) is the culmination of a
rhombohedral submarine structure on the shelf area.
The flanks of the NAR display important gradients (up
to 57°) more abrupt (8-27°) in the north-eastern sector,
meanwhile the central and south-western sector gradients are gentler, ranging (2-24°). The base of the
northern flank is located at depths of approximately
1,400-1,700 m water and in the southern flank varies
from water depths of 1,160 to 1,060 m. The main morphological features identified on this seamount are:
erosive terraces, crests, tectonic scarps and depressions, as well as sedimentary waves on the top of the
shelf (Bárcenas et al., 2004a,b), and scars, massmovement deposits, linear erosive features (e.g.,
canyons, gullies) and contourite deposits, ridges and
valleys sets and a intraslope marginal plateau on the
flanks.
Several erosive terraces have been located in the
north-eastern sector of the top of the shelf and they
could be grouped at least four levels at water depths
of between 65 and 90 m (Bárcenas et al., 2004a,b).
Minor crests (between 1 and 6 km in length and 1.5 to
25 in height) associated to basement outcrops have
been differentiated in the north-eastern sector
(Bárcenas et al., 2004a,b). Tectonics scarps and
depressions of ENE-WSW, WNW-ESE, NW-SE and
NNE-SSW trends are related to faults (MaestroGónzalez et al., 2008). Sedimentary waves may
appear as solitary features around the main reliefs or
grouped in a field on the southern part of the shelf
(Bárcenas et al., 2004a, b).
Scars (3 to 10 km in length sub-parallel to the
flank) and mass-movement deposits (from slides to
turbidites) are more developed on the southern flank
where two short NNW-SSE canyons (7 km length)
also occur (Bárcenas et al., 2001), however a large
arc-shaped feature on the northern flank of the central
and north-eastern sectors has been interpreted as the
header scar of an old slide (Martínez-García et al.,
2011). Linear erosional features, oriented NNW-SSE
to N-S, occur on the northern flank of the north-eastern sector of the NAR, where a major canyon (9.5 km
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Figure 4. The North Alboran Ridge (SE-Iberian) : (A) physiographic domains of the Alboran Sea Basin (EAB: Eastern Alboran Basin; WAB:
Western Alboran Basin; MP: Marginal Plateau), (B) Bathymetric and tectonic map (AF: Averroes Fault; AIF: Al Idrissi Fault; DMFS: DjiboutiMotril Fault System; YF: Yusuf Fault), (C) Slope gradients and geomorphological map showing the main structural, mass-movement and
bottom current features, and (D) Airgun high-resolution seismic profile crossing the North Alboran Ridge (see location on Fig. 4B). Legend:
MPR, Mid-Pleistocene Revolution; BQ, Quaternary Base; LPR, Lower Pliocene Revolution; M, Pliocene Base; CU, contouritic deposits; mtd;
mass transport deposits; MR, multiple reflector; twtt in seconds.
Figura 4. Dorsal de Alborán Septentrional (SE-Iberia): (A) Dominios fisiográficos de la cuenca del Mar de Alborán (EAB: Cuenca Oriental
de Alborán; WAB: Cuenca Occidental de Alborán; MP: Plataforma Marginal), (B) Mapa Batimétrico y Tectónico (AF: Falla de Averroes; AIF:
Falla de Al Idrissi; DMFS: Sistema de fallas de Djibouti-Motril; YF: Falla de Yusuf), (C) Mapa de Pendientes y de los principales rasgos geomorfológicos de tipo estructural, movimientos en masa y corrientes de fondo y (D) Perfil sísmico de alta resolución (cañones de aire) atravesando la Dorsal de Alborán Septentrional (localización en la Fig. 4B). Leyenda: MPR, Revolución del Pleistoceno Medio; BQ, Base del
Cuaternario; LPR, Revolución del Plioceno Inferior; M, Base del Plioceno; CU, depósitos contorníticos; mtd, depósitos de transporte en
masa; MR, Reflector múltiple.
long and 0.6 km wide) and several secondary canyons
(3-5 km in length) and gullies (0.7 km in length) have
been identified.
Two sets of ridges and valleys have been differentiated, the first one is an E-W set located in the northern flank of the north-eastern sector (15 km in length)
and is related to the northern boundary faults of the
NAR, and the second set is a series of ridges and val-
leys of NNE-SSW mapped on the western boundary
of the NAR. These reliefs have been interpreted as a
consequence of the Quaternary activity of the Al
Idrissi fault (Gràcia et al., 2010; Martínez-García et al.,
2013). The upper slopes of the northern flank of the
central and south-western sector are linear and
abrupt linear but an intraslope marginal plateau
occurs on the middle slope (0.4-3°) at 400-800 m
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Figure 5. The Banks of Djibouti on the Alboran Sea (SE- Iberian) : (A) Bathymetric map, (B) Geomorphological map showing the main structural, fluid escape, mass-movement, bottom current and biogenic features and (C) Sparker seismic profile crossing the Avempace and La
Herradura banks. Legend: MPR, Mid-Pleistocene Revolution; BQ, Quaternary Base; LPR, Lower Pliocene Revolution; M, Pliocene Base. Fig.
5B is modified from Palomino et al., (2011).
Figura 5. Bancos de Djibouti en el Mar de Alborán (SE-Iberia): (A) Mapa Batimétrico, (B) Mapa Geomorfológico mostrando los principales
rasgos estructurales, escape de fluidos, movimientos en masa, corrientes de fondo y estructuras biogénicas y (C) Perfil sísmico de Sparker
a través de los Montes submarinos de Avempace y Herradura. Leyenda: MPR, Revolución del Pleistoceno Medio; BQ, Base del
Cuaternario; LPR, Revolución del Plioceno Inferior; M, Base del Plioceno. La Fig. 5B está modificada de Palomino et al., (2011).
water depth) where plastered drift deposits and a discontinuous moat are defined over the marginal
plateau (Fig. 4D) (Ercilla et al., 2012).
Most of the Djibouti Banks (summits at 200-500 m
water depth) display truncated cone geometries,
except in the case of the Herradura Spur Smt. which
is pyramid-like in shape. They occupy areas of around
73-83 km2, with the exception of the La Herradura
Bank which is greater in extent (202 km2). The tops of
these seamounts are relatively flat (< 5°) and their
flanks display higher slope gradients (up to 53°)
(Table 1). The main morphological features identified
on these seamounts are: crests, terraces, gullies,
slides, mass movement deposits, and contourite
deposits (Fig. 5B). Minor NNE-SSW scarps cross
these seamounts as is the case of the La Herradura
Banks: these scarps are related to the Quaternary
activity of the Djibouti-Motril fault system.
Outcropping crests and superimposed biogenic features composed of carbonate-rich sediments are
496
found on the top (Fig. 5B, C). Several terraces (up to
6.5 km in length) have been identified on the top-flank
at various water depths (280 m to 450 m) and on the
south-western flank of the La Herradura Bank. Several
gullies (2 km in length and 1.5 km in width) occur on
variably steep slopes (5° to 20°) on the La Herradura
and Avempace banks and are radially oriented in relation to the summits (Fig. 5B). Small (2 km2) and moderate-sized (13 km2) slides have been identified mainly on the southern flank of the La Herradura Bank (300
m to 800 m water depth). The four seamounts are surrounded by narrow contouritic moats (1-2 km in width
and 5.5-10 km in length) as well as drifts (Palomino et
al., 2011) (Fig. 5B).
Genetic processes
The seamounts studied in the Alboran Sea formed in
two main episodes. One period corresponds to the
Late Oligocene-Miocene extension which generated
structural highs sub-parallel to the back-arc trend and
volcanoes, which are part of the highest summits in
this basin, particularly in the eastern Alboran region
(Comas et al., 1999). The other period is related to the
Late Miocene to present compression (MartínezGarcía et al., 2013), which is responsible for the latest
elevation of the main seafloor reliefs. On the NAR,
volcanism involving tholeiitic basaltic andesites (Gill
et al., 2004) dates from 9.4 to 9.3 Ma, indicating that
the eastern sector of this high, around the Alboran
Island, was an active volcanic edifice during the Late
Miocene (Fernández Soler et al., 2000; Duggen et al.,
2004). A last compressive phase produced a shortening of the orogenic systems, mountain uplift on the
main land, reduction of the initial Alboran Sea Basin,
tilting of basement margins and the structural uplift
of previous basement morphological highs
(Avempace Bank) and other, volcanic features (the La
Herradura, La Herradura Spur and Djibouti Ville
banks). This phase involved the formation of the NAR
as a tectonic relief, uplifted by means of folding and
laterally-compressive faulting that follow the same
ENE-WSW trend as the seamount, including previous
Miocene volcanic elements such as the Alboran
Island (Bourgois et al., 1992; Vegas, 1992b; Woodside
and Maldonado, 1992; Watts et al., 1993).
instabilities on the flanks, and debris flow deposits at
the foot of the slope and current tectonic activity.
Dense deep Mediterranean water masses and intermediate waters (including the Winter Intermediate
Water and Levantine Intermediate Water) interact
with the seamounts favouring the formation of moats
at the foot and the associated drift deposits (Fig. 2).
Elongated and plastered drifts have been described
around the Djibouti Banks (Palomino et al., 2011),
whereas on the north-western flank of the NAR only
plastered drifts have been identified (Ercilla et al.,
2012). Other processes related to water-mass dynamics include the presence of several guyots, some of
them corresponding to current isolated shelves (NAR,
Xauén Bank) characterised by carbonate sedimentation, particularly coralline algae and rodoliths related
to Atlantic water flow and sea level oscillations
(Milliman et al., 1972; Bárcenas et al., 2001). The sedimentary instabilities that produce mass movements
at various scales are evidenced by slide scars on the
seamount flanks and debris flow deposits at the foot
of the slope. These are evident on the southern flank
of the NAR, where several mass movement deposits,
varying from slides to turbidites, have been identified
(Vázquez et al., 2010). The intense sedimentary instability processes are related to continuous moderate
seismic activity (Stich et al., 2006) and the reactivation
of relief gradients caused by Quaternary tectonics.
Several tectonic structures show current activity in
this area: i) inverted characteristics on the eastern
sector of the northern flank of NAR (Estrada et al.,
2014), ii) Quaternary movements in the NW-SE Yusuf
fault to the east of the NAR, as well as in the Averroes
and Adra fault systems on the Djibouti-Motril marginal plateau (Gràcia et al., 2012; Estrada et al., 2014;
Vázquez et al., 2014), and iii) a modern left-lateral
NNE-SSW trending strike-slip fault system cuts the
main reliefs, in this sense the Al Idrissi fault divides
the Alboran Ridge into two parts and also generates
two sets of ridges and valleys with the same trend
(Gràcia et al., 2010; Martínez-García et al., 2013), and
the Djibouti-Motril fault system affects the Djibouti
Banks (Vázquez et al., 2008b).
Seamounts in the Gulf of Cadiz
Morphology
The main geological processes affecting the NAR and
the Djibouti Banks are: bottom current activity and its
interference with the seamounts and sedimentary
Four seamounts (Guadalquivir Bank, Portimao Bank,
Cadiz Diapiric Ridge and Guadalquivir Diapiric Ridge)
have been recognised in the Gulf of Cadiz (numbers
27, 28, 50 and 51 in Fig. 1). In this section, two main
seamounts (numbers 27 and 28 in Fig. 1),
497
Guadalquivir Bank (27) and Portimao Bank (28) (Figs.
6 and 7, Table 1), are described because of their
oceanographic and geological location in the northern part of the Gulf of Cadiz. The Guadalquivir Bank is
an isolated high, located at the edge of the continental slope of the distal Portuguese margin, 75 km to the
south Portuguese coast (Vegas et al., 2004). The
Portimao Bank or Plateau, described as the westernmost part of the Guadalquivir Bank (Terrinha et al.,
2009; Matias et al., 2011), is also located at the edge
of the continental slope of the southern Portuguese
margin, about 100 km from the coast.
The Guadalquivir Bank trends NE-SW, is elongated
in shape, and occupies an area of 82 km2 (11.2 km
long and 8.75 km wide) (Table 1) with two summits at
different water depths (275 m in the northeast and
410 m in the southwest). The top is relatively flat (3°)
and the flanks have higher slope gradients (up to 40°).
The main morphological features identified on this
bank are: crests, terraces, scarps, slides, gullies, biogenic mounds, moat and drift deposits (Fig. 6 B, C, D).
These features have a NE-SW main trend, except the
slides and gullies, which are NW-SE. The crests and
terraces appear on the top whilst the scarps, slides,
and gullies are located on the southern flank. The
Guadalquivir contouritic channel is oriented ENEWSW and is around 4 km wide, and a deformed contouritic drift bounds the southern base of this bank
(Llave et al., 2007a, b) (Fig. 6 B, C, D). Towards the
northwest a second countouritic channel (0 to 2 km
wide) developed from northeast to southwest bounds
the southern base and separates the bank from the
Bartolomeu Dias Plateau (Fig. 6 B, D).
The Portimao Bank (summit at 1,500 m water
depth) is W-E trending, has an elongated shape and
occupies an area of about 1,800 km2 (93 km long and
15-28 km wide) (Fig. 7A). The top is flat (approximately 0.2°) in the eastern sector, whilst in the central
and western sector gradients are higher (2°-4°). The
top increases in depth towards the west, from 1,500
to 3,500 m. The slope gradient increases on the flanks
(4-15°). The southern flank is the steepest (12°-15°)
and presents escarpment morphology, whilst the
north-eastern flank is less steep (4-5°). The main morphological features identified on this bank are: crests,
depressions, bulges, domes on the top, slide scars
and mass movement deposits, and escarpments on
the flanks (Fig. 7 B, C). In particular, a 32 km-long crest
feature oriented W-E has been mapped on the top
towards the north of the bank, probably related to
recent tectonics and salt mobility (Terrinha et al.,
2009; Matias et al., 2011). Two bulges have been identified in the central sector of the bank top, the most
prominent being related to the Don Carlos Diapir
(Terrinha et al., 2009). This is a circular dome-shaped
area (47 km2) rising around 320 m above the high and
surrounded by a circular depression (Fig. 7B). This
feature marks the boundary between the western and
eastern structural styles of the bank. The other bulge,
located 4 km towards the northwest of the Don Carlos
diapir, is cone-shaped, occupies a smaller area (2.5
km2) and is 100 m high. Slide scar features are located on the northern and southern flanks, those in the
north being smaller (4-5 km in length and 1.5-2 km in
width) than those located on the southern flank (17
km in length and 1-3 km in width). These slide scars
seem to originate from the Don Carlos diapir, extending downslope on the southern flank. Escarpments
are identified on the north-eastern part of the
Portimao Bank, which are 28 km long and rise 170 m
above the seafloor (Fig. 7B).
Genetic processes
The southern Portuguese margin acted as the northern boundary, in the Gulf of Cadiz, of the compressive
western front of the Betic-Rif orogen. The current
structure and morphology of the Guadalquivir Bank is
a relict of its evolution in a rift-transcurrent margin
type (Medialdea, 2007), and Paleozoic rocks have
been dredged (Vegas et al., 2004). Nevertheless, the
last important uplift is related to the Betics-Rif development and occurred in the Late Tortonian to Early
Messinian, and even during the Pliocene-Quaternary
as revealed by anticlinal and synclinal folds affecting
Pliocene and Pleistocene sedimentary units along the
south-eastern flank of this bank (Gràcia et al., 2003;
Medialdea et al., 2004). Seismotectonic activity has
been described by Negredo et al. (2003) and is characterised by shallow and intermediate depth seismic
events which present reverse faulting with a strikeslip component and horizontal NNW-SSE compression. Structurally, the Portimao Bank has been interpreted as a pop-up structure (Terrinha et al., 2009)
related to thrust faults resulting from the tectonic
inversion of Mesozoic rift faults (Mougenot et al.,
1988, Zitellini et al., 2004, Duarte et al., 2011) with
marked diapiric activity. A basement high has been
observed in the south-eastern sector that has been
interpreted as a reactivated reverse fault which uplifted Pliocene-Quaternary units, and in the northern
sector a crest delimited at the seafloor surface, generated by an anticlinal fold related to a blind thrust or
diapirism, has caused deformation of the current sedimentary units (Vázquez et al., 2013).
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Figure 6. The Guadalquivir Bank of the Gulf of Cadiz margin (SW-Iberian): A) Bathymetric map, B) Geomorphological map showing the
main structural, mass-movement, mixed, biogenic and bottom current features, and (C, D) Sparker seismic profiles showing the architectural features. MPR, Mid-Pleistocene Revolution; BQD, Quaternary Base Discontinuity; M, Pliocene Base.
Figura 6. Banco del Guadalquivir en el margen del Golfo de Cádiz (SO-Iberia): (A) Mapa batimétrico, (B) Mapa geomorfológico mostrando los principales rasgos estructurales, de movimientos en masa, mixtos, biogénicos y de corrientes de fondo, y (C, D) Perfiles sísmicos
de Sparker mostrando los rasgos arquitectónicos. MPR: Revolución del Pleistoceno Medio; BQD: Discontinuidad de la Base del
Cuaternario; M: Base del Plioceno.
The two Gulf of Cadiz seamounts studied play an
important role in the morphostructure and architecture of the margin, as well as modifying sedimentary
and oceanographic processes due to their geographic location (Figs. 1, 2, 6 and 7). Structurally, the southern sector of the Guadalquivir Bank acts as an obstacle for the advance of the Gulf of Cadiz allocthonous
unit (Medialdea et al., 2004), emplaced during the
Tortonian, and therefore in some way it controls the
detachment and elevation of the thrust wedges which
deformed this unit. A Pliocene-Pleistocene uplift
episode is evidenced by the south-eastern scarp of
the Guadalquivir Bank that displaces the lateral ramp
of the allocthonous unit (Medialdea et al., 2004). To
the northwest the Portimao Bank constitutes also a
barrier to the sediment flow supplied by the
Portuguese margin mainly through the Portimao
Canyon and the Faro Canyon, meanwhile the northern sector of the Guadalquivir Bank is covered by the
Neogene-Quaternary Bartolomeu Dias Drift, which is
related to the Mediterranean Outflow Water (MOW)
(Llave et al., 2001; Hernández-Molina et al., 2006;
Roque et al., 2012) (Fig. 6). On the southern flank,
since the Pliocene, the MOW has eroded and shaped
499
Figure 7. The Portimao Bank of the Gulf of Cadiz margin (SW-Iberian): (A) Bathymetric map (from SWIM bathymetric data base, Zitellini
et al., 2009), B) Geomorphological map showing the main structural, mass-movement, mixed, and bottom current features, and (C)
Sparker seismic profile showing the architectural features.
Figura 7. Banco de Portimao en el margen del Golfo de Cádiz (SO-Iberia): (A) Mapa batimétrico, (de la base de datos batimétricos SWIM,
Zitellini et al., 2009), (B) Mapa geomorfológico mostrando los principales rasgos estructurales, de movimientos en masa, mixtos, biogénicos y de corrientes de fondo, y (C) Perfil sísmico de alta resolución (cañones de aire) mostrando los rasgos arquitectónicos.
the Guadalquivir contouritic channel (HernándezMolina et al., 2006; Llave et al., 2007a; García et al.,
2009; Hernández-Molina et al., 2014). Instabilities and
mass movement processes are responsible for the
slide scars located on both flanks of this bank. On the
southern flank, the slide scars are mainly linked to
recent and present-day diapirism, whereas the slide
scars and escarpment on the northern flank are both
related to the uplift of blind thrusts (Terrinha et al.,
2009).
Seamounts in west Portugal
Morphology
Six main seamounts (Coral Patch Seamount, Coral
Patch Ridge, Ampere Smt., Gorringe Bank, Hirondelle
Smt. and Tore Smt.) have been identified to the west of
Portugal (numbers 29 to 33 and 52 in Fig. 1). Three
seamounts (numbers 29, 31 and 33 in Fig. 1), selected
due to their large dimensions, are described here: the
500
Coral Patch Smt. (29), the Gorringe Bank (31) and the
Tore Smt. (33) (Fig. 8, Table 1). The Coral Patch Smt. is
located southwards of the SWIM Fault Zone (Rosas et
al., 2012) (Fig. 1). It is limited to the north by the
Horseshoe Abyssal Plain, to the south by the Seine
Abyssal Plain, and to the west by the Ampere Smt.
(Fig. 1). The Gorringe Bank, the major morphological
feature of the south-western Iberian margin (Auzende
et al., 1978), is located approximately 120 km WSW off
Cape Saint Vicente (Fig. 1). To the south it is surrounded by the Horseshoe Abyssal Plain at depths of 4,800
m, and to the north by the Tagus Abyssal Plain which
reaches depths of 5,100 m (Fig. 8B). This seamount is
located northwards of the SWIM Fault Zone (Zitellini et
al., 2009), and is considered as one of the main seismogenic sources in southwest Iberia (Borges et al.,
2001). This feature is also associated with one of
largest positive free-air gravity anomalies in the world
(300 m Gal) and a 9 m positive gravity anomaly in the
geoid (Souriau, 1984). The Tore Smt., the least known
seamount of the western Iberian margin, is located
approximately 300 km west of the Portuguese coast. It
Figure 8. Seamounts of the Atlantic oceanic domain (W-Iberian): Bathymetric maps of the (A) Coral Patch Smt., (B) the Gorringe Bank (both
from SWIM bathymetric data base, Zitellini et al., 2009), and (C) the Tore Smt. (the bathymetric metadata and Digital Terrain Model data
products have been derived from the EMODnet Hydrography portal-http://www.emodnet-hydrography.eu), and (D) photos of the sedimentary cover on the Coral Patch Smt. displaying fragments of (1) deep-water corals, (2) bioclastic sands and (3) fragment (~40 cm long)
of pillow-lava with pelagic carbonates filling the veins.
Figura 8. Montes submarinos del dominio oceánico Atlántico (O-Iberia): Mapas batimétricos de (A) el MS de Coral Patch, (B) del Banco de
Gorringe (de la base de datos batimétricos SWIM, Zitellini et al., 2009), (C) del MS de Tore (los metadatos batimétricos y el Modelo Digital
del Terreno proceden del portal EMODnet Hydrography-http://www.emodnet-hydrography.eu), y (D) Fotos de la cobertera sedimentaria
sobre el MS de Coral Patch mostrando fragmentos de (1) corales de aguas profundas, (2) arenas bioclásticas y (3) fragmentos (~40 cm de
longitud) de lavas almohadilladas con carbonatos pelágicos en venas rellenando fisuras.
501
is bounded to the north by the Iberian Abyssal Plain
and to the south by the Tagus Abyssal Plain (Figs. 1
and 7C). It represents the northern end of the ToreMadeira Rise, a ~1,000 km long submarine volcanic
elevation crossing the Eurasian and African plates
(Merle et al., 2006; Miranda et al., 2009).
The Coral Patch Smt. (summit at 560-750 m water
depth) is WSW-ENE trending, has an elongated shape
and occupies an area of 8,400 km2 (120 km long and
70 km wide) (Table 1). The slope of the western flank
is gentle (< 5°), whereas the south-eastern flank is
steeper (5°-20°) (D’Oriano et al., 2010). The main morphological and structural features identified on this
seamount are: volcano thrust-faults, linear scours,
scarps, and ridges. Nine small volcanoes have been
mapped on the summit using swath bathymetry and
ROV images. These minor volcanic edifices reach
widths of 3-5 km and heights of 100-300 m, but the
largest has a diameter of about 8 km. These features
are well preserved and present typical sub-circular
and conical shapes with associated radial features on
the slopes, and have been interpreted as lava flows
(D’Oriano et al., 2010). A major WSW-ENE thrust-fault
overthrusts the Horseshoe Abyssal Plain towards the
north and limits the northern flank (Martinez-Loriente
et al., 2013). Small linear scours cut the eastern sector
of the flanks, whilst the shallower central part presents a flat area and the deeper section displays several northward-verging scarps (D’Oriano et al., 2010).
A series of sub-parallel crests spaced from 1.5 to 4.0
km, trending NE-SW have been identified in the
north-western area of this seamount. These features
reach 15-50 km in length, 2-3 km in width and heights
of ~100 m. The crests correspond to large-scale folds
with wavelengths of ~20 km, associated with steep
faults affecting the uppermost sediments and the
seafloor (Martínez-Loriente et al., 2013).
The Gorringe Bank (summit at 20 m water depth)
has a NE-SW trending elongated ridge and occupies
about 14,000 km2 (200 km long and 70 km wide) (Table
1). It is formed by two minor seamounts, the
Ormonde Smt. (summit at 33-46 m water depth) in
the northeast and the Gettysburg Smt. (summit at 2028 m depth) in the southwest (Fig. 8B). The average
slope gradients of the flanks range from 5° to 10°, but
higher values are observed locally. The south-eastern
flank of the Ormonde Smt. has gradients of up to 20°,
whereas on the north-western flank they reach 30°. A
clear depositional shelf break can be seen at 140 m
depth, and locally an erosional shelf break occurs
between 130 and 170 m depth characterised by
increasing gradients (> 6°-8°) (De Alteriis et al., 2003).
The main morphological and structural features identified on this seamount are: terraces, slope failures
and a thrust-fault. The terraces display sub-horizontal
surfaces (< 3°-4°) at depths of between 60 m and 100120 m, which were probably generated during the
partial emersion of the Gorringe Bank in the Last
Glacial cycle (De Alteriis et al., 2003; Ferranti et al.,
2014). Several scars related to slope failures have
been located on both flanks of this seamount with a
sub-parallel trend. On the northern flank, one of these
scars has been associated with a main landslide
deposited as an avalanche at the foot of slope of the
seamount (Lo Iaccono et al., 2012). The northern flank
is bounded by a major northward-verging thrust-fault
(Terrinha et al., 2003).
The Tore Smt. (summit at 2,300 m water depth)
trends NE-SW to NNE-SSW, and has an elongated
shape enclosing a central elliptical depression, the
Tore Basin (Fig. 8C). This complex seamount occupies a very broad area, 31,000 km2 (239 km in length
and 130 km wide) and to the east is morphologically
connected to the Estremadura Spur by means of four
E-W ridges, the Egas Moniz Ridges, which are asymmetric highs trending E-W to WNW-ESE, and varying
from 46 to 90 km in length. The summits of these
ridges are deeper towards the north, ranging from
about 3,050 m water depth in the south to 4,540 m in
the north. The Egas Moniz Ridges and the eastern
flank of the Tore Seamount enclose a small basin
about 4,900 m deep, known as the Pomba Basin (Fig.
8C). The main morphological and structural features
observed on this seamount are crests and isolated,
volcanically-originated small seamounts, arranged in
E-W to ENE-WSW trends, and which have summits
between water depths of 2,300 and 3,000 m (Roque
et al., 2009). These features surround the central
asymmetric NE-SW-trending Tore Basin (Fig. 8C).
Genetic processes
The genesis and formation of the Coral Patch Smt. is
linked to Cenozoic magmatism (32 Ma) that probably
represents the trace of the Madeira hotspot
(Geldmacher et al., 2005; Merle et al., 2009;
Geldmacher et al., 2011). This seamount is part of the
larger Coral Patch Ridge-Coral Patch Smt. which has
been recently described by Martínez-Loriente et al.
(2013; 2014). The Pliocene and Quaternary convergence between the African and Eurasian plates
deformed the basement and the uppermost sediment
cover, forming faults and folds (Hayward et al., 1999).
This compression was accommodated by the northwards thrusting of the Coral Patch Smt. over the
Horseshoe Abyssal Plain (Martínez-Loriente et al.,
2013; 2014).
502
The Gorringe Bank has been studied for many
years, due to the interest in its main size and gravity
anomaly (Auzende et al., 1978), alkaline volcanic
rocks have been dragged from it but it corresponds to
a structural high constituted as both oceanic basement (Féraud et al., 1986) and serpentinized peridotite
(Sallarés et al., 2013). It has a long geodynamic history, and it has recently been proposed that it was
formed in a Late Jurassic transtensional phase
(Jiménez-Munt et al., 2010; Sallarés et al., 2013). On
the southern flank of the Ormonde Smt, the oceanic
basement gabbros have been intruded by a few
doleritic sills (Girardeau et al., 1998a,b; Girardeau et
al., 1998b) and covered by younger alkali-basalt lavas
(Schärer et al., 2000). The intrusion of these alkaline
rocks is related to the Late Cretaceous alkaline magmatism that affected western Iberia (Cornen, 1982;
Bernand-Griffith et al., 1997; Miranda et al., 2009), in
about 67-65 Ma (Féraud et al., 1986) or 66-60 Ma
(Schärer et al., 2000). Volcanic rocks retrieved from
the Ormonde Smt., such as alkali basalts, nephelinites, nephelinesyenites, tinguaites, phonolites and
monchiquites, are similar to those found onshore on
the Monchique and Sines sub-volcanic massifs
(Cornen, 1982; Bernand-Griffith et al., 1997), and have
been suggested as being part of the MonchiqueOrmonde-Madeira hot-spot track (Geldmacher et al.,
2006). The Gettysburg Smt. has been interpreted as
having formed due to deformation of the serpentinized basement (De Alteriis et al., 2003; Ferranti et
al., 2014). Finally, during the Eocene-Miocene compressional phases, the Gorringe Bank was affected by
tectonic reverse faulting, overthrusting northwards
towards the Tagus Abyssal Plain (Terrinha et al., 2003;
2009) along the deep thrust-fault that bounds its
northern flank. Present-day clustering of earthquake
epicentres in this feature indicates recent tectonic
activity (Borges et al., 2001).
The genesis and formation of the Tore Smt. has
been explained by three different hypotheses: i) a
giant caldera caused by the collapse of a super volcano into its magma chamber, ii) a meteorite impact
crater, and iii) a mixture of tectonic trends (Laughton
et al., 1975; Monteiro et al., 1998; Ribeiro, 2002).
Alkaline rocks have been dredged along the Tore
seamount and related features consist of basalt, trachyte, diorite, granodiorite, and breccias, ranging in
age between ~104.4 Ma and ~80.5 Ma (Merle et al.,
2006). These volcanic rocks and new data acquired as
part of the Portuguese Continental Shelf Extension
project show that the morphology of this seamount
seems to be due to the conjugation of Late
Cretaceous magmatic activity and tectonics (Roque et
al., 2009). The Late Cretaceous saw the emplacement
of alkaline volcanism along ~E-W to NNE-WSW fractures, clusters of small seamounts with the same orientation, and volcanoes aligned ~E-W to WNW-ESE
(Roque et al., 2009). This alignment suggests a channelling and extrusion of the alkaline magmas through
deep-faults with this orientation (Merle et al., 2009)
that work as a secondary transfer system for the continental break-up, as has been suggested by several
authors (Tucholke et al., 2007). These structures were
reactivated as thrust-faults during the Cenozoic as a
consequence of the Alpine orogenic phases associated with the formation of the Pyrenean and Betic
chains. Lastly, Pliocene and Quaternary deformation
can be related to the post-Tortonian reorganisation of
the Eurasian-African plate boundary (Roque et al.,
2009).
Several episodes of slope failure and mass movement have been identified on the flanks of the three
eastern Iberian margin seamounts studied (Roque et
al., 2009; D’Oriano et al., 2010; Lo Iaccono et al., 2012).
A major episode of mass movement can be seen on
the northern flank of the Ormonde Smt. (Gorringe
Bank), evidenced by a large slope scar at a water
depth of between 2,900 and 5,100 m. This episode
would have originated an avalanche comprising ~80
km3 of material and 35 km runout (Lo Iacono et al.,
2012). These authors simulated a near-field tsunami
for the volume of displaced sediments, and calculated that a wave more than 15 m high would have been
generated, which would have hit the southern
Portuguese coast less than 30 minutes after the
occurrence of the landslide (Lo Iacono et al., 2012).
Numerous amphitheatre scarps and slumps have
been identified on the flanks of the Tore Smt. and also
within the stratigraphic succession of Tore Basin
(Roque et al., 2009). There is also evidence of bottomcurrent activity, including ripples and scours,
observed during ROV dives on the south-eastern
flank of the Coral Patch Smt. (Wienberg et al., 2013).
Lastly, the summits of the Gorringe Bank were affected by erosive processes related to a sea level fall that
favoured terrace formation (Ferranti et al., 2014).
Seamounts on the Galicia margin
Morphology
Five main seamounts (Porto, Vigo, La Coruña and
Finisterre seamounts and Galicia Bank) have been
503
identified in the Galicia matgin (numbers 34 to 38 in
Fig. 1), as well as at least thirteen smaller features
(Vanney et al., 1979; Ercilla et al., 2006, 2008b, 2011)
(Fig. 9A). In this section, only the Galicia Bank (36 in
Fig. 1) is described as it is the most relevant
seamount due to its size. This bank is located in the
distal domain of the western Galician continental
margin (north-western Iberian margin), about 200 km
from the coast (Fig. 1) and is considered a major
structural seamount controlled by two Mesozoic fault
families: N-S to NW-SE trending normal faults and
NE-SW transfer faults (Boillot et al., 1989; Vázquez et
al., 2008a).
The Galician Bank (summit at 605 m water depth)
is a plateau-like feature with quasi-rhombohedral
geometry (84 km long; 60 km wide) that occupies an
area of 2,946 km2 (Fig. 9). The top is a smooth, asymmetric, low-mound surface (1°-2.5° but locally up to
5°). This plateau has sharp boundaries with steep
flanks (17-40°). The main morphological and structural features observed on this bank are (Ercilla et al.,
2011): erosive furrows, an abraded plain, biogenic
mound-shaped features, plastered drifts and sediment waves on its top; gullies on the flanks; and a
moat and associated elongated drift at the foot of the
flanks (Fig. 9B). The erosive furrows are mainly located at the south-western periphery of the plateau (8252,100 m water depth) and appear as numerous NNWSSE linear depressions spaced between 1,200 and
1,600 m apart. They display U- or V-shaped cross-sections (0.5 to 1.5 km wide and a few metres to 10 km
long). The abraded plain (<1° to 10°) has been defined
on the south-western periphery of the plateau. The
plastered drift deposits blanket the wall of the western flank and the crest of the plateau at a water depth
of between 768 and 1,400 m. These latter deposits
have an E-W trending, step-shaped profile facing
westward, and a N-S mound geometry (gradients 0°2.5°, locally up to 5°). Small (< 7 m relief, hundreds of
metres wave length) and large scale sediment waves
(55-65 m relief and 1.5 km wave length) affect these
plastered deposits. Finally, biogenic mound-shaped
feature have been identified on the periphery of the
bank top (700 to 1,125 m), which appear as ridges (a
few kilometres to 25 km length) with reliefs of up to
200 m, and widths of around 500 m (Ercilla et al.,
2011; Somoza et al., 2014). The flanks are characterized by scarps. They have reliefs of between 600 and
2,000 m, are 15 to 50 km in length, with variable orientations (NW-SE, N-S, and NE-SW). Numerous erosive gullies, seen as narrow V-shaped incisions separated by sharp ridges (hundreds of metres wide, ≈1 to
< 5 km long, and from a few to tens of metres in
relief), affect the flanks. At the foot of the south-east-
ern flank of the Galicia Bank, a 33-km long moat has
been identified that runs parallel to the bank. The
moat has an asymmetrical U-shaped cross-section
that decreases in width northwards (8.5 to 1.7 km)
while increasing in relief (35 to 55 m). Associated to
the moat, a mounded and separated elongated drift
has been defined (Fig. 9B).
Genetic processes
The early genesis of the Galicia Bank must be related
to the formation of the rifted margin, as evidenced by
the Mesozoic normal blocks that constitute the main
structures around the bank, as well as by the presence of Cretaceous volcanic rocks and pre-Mesozoic
metamorphic and granitic basement. Originally this
feature would probably have been a main horst. The
exhumation of these geological units and the present
regional morphostructure is a result of Mesozoic rifting phases and later Eocene-Miocene compression
(Boillot et al., 1989). The bank can be explained as
part of a major antiform related to the north-western
thrust of the margin corresponding to the subduction
of the western end of the Bay of Biscay, in the context
of the Pyrenean orogeny (Sibuet et al., 2004). The prevailing morphology corresponds to the interference
of the regional uplift and the reactivation of Mesozoic
normal faults during Pyrenean tectonics. The
Cenozoic reactivation of normal faults affected the
relief, particularly the scarps making up the flanks of
the Galicia Bank (Vázquez et al., 2008a).
The Galicia Bank is affected by various transport
modes: downslope and the more dominant alongslope processes (Ercilla et al., 2011). The downslope
processes are mainly represented by turbidity flows
and related flows which dominate on the flanks of the
bank. These processes are responsible for gully formation. The alongslope processes erode, redistribute
and winnow the seafloor sediments of the Galicia
Bank plateau, developing erosional (furrow and
abraded plain) and depositional (plastered drift and
sand wave) features. These features are also present
at the foot of the eastern and northern scarps where
the influence of bottom currents produces a moatelongated drift system. The contourite deposits are
generated by the MOW (Fig. 2). The contour-current
hemipelagic deposits mainly result from the interaction of hemipelagic settling with low-velocity MOW
and LSW. There are also several features related to
504
Figure 9. The Galicia Bank of the Galician margin (NW-Iberian): (A) Physiographic and tectonic map of the Galicia Bank region, and (B)
Geomorphological map showing the main structural, fluid-dynamic, mass-movement, and bottom current features. Fig. 9A has been modified from Vázquez et al. (2008) and Fig. 9B from Ercilla et al. (2011).
Figura 9. Banco de Galicia en el Margen de Galicia (NO-Iberia): (A) Mapa Fisiográfico y Tectónico de la región del Banco de Galicia y (B)
Mapa Geomorfológico mostrando los principales rasgos estructurales, de dinámica de fluidos, de movimientos en masa y de corrientes
de fondo. La Fig. 9A ha sido modificada de Vázquez et al. (2008) y la Fig. 9B de Ercilla et al. (2011).
505
biogenic cold water coral constructions (Ercilla et al.,
2011; Cartes et al., 2014; Somoza et al., 2014).
Seamounts on the Cantabrian margin
Morphology
Eight main seamounts (Vizco High, Le Danois Bank,
ECOMARG High, Santander Promontory, Landes,
Jovellanos, Charcot and Vizcaya Smt.) have been
described on the Cantabrian continental margin and
the Bay of Biscay (numbers 39 to 46 in Fig. 1). Here,
the Le Danois Bank (40) is described as it constitutes
a first order feature of the continental margin physiography and has recently been declared Spain’s first
‘Marine Protected Area’ (Sánchez et al., 2008; 2009)
(Fig. 1). The Le Danois Bank, also called “The
Cachucho” by local fishermen, was described for the
first time in the 1948 book ‘Les Profondeurs de la Mer’
by the French scientist Edouard Le Danois. It is located 70 km to the north of the Cantabrian continental
margin on the Asturian Marginal Plateau (Fig. 10).
The positioning of the Le Danois Bank creates an
intra-slope basin to the south (Asturian Intra-slope
Basin) parallel to the margin and dipping toward the
east (from 920 to 2,050 m water depth) (Fig. 10).
The Le Danois Bank (summit at 550 m water depth)
is W-E trending, has an elongated shape, and occupies an area of 1,150 km2 (72 km long and 15 km wide)
(Table 1). Its top is relatively flat (< 2°). The flanks have
moderate slope gradients (16.5° to 18° in the north;
about 12° in the south) (Table 1). The main morphological features and deposits recognised on this
seamount are (Fig. 10): gullies, slides, slide scars, a
turbidite channel, and contourite features. Gullies and
slides are observed mainly on the northern flank,
whereas slide scars and a wide range of mass-movement deposits are identified along the northern and
southern flanks. The Le Danois turbidite channel runs
along the south-eastern base of the bank and mouths
onto the lower slope as a hanging channel (Van Roij
et al., 2010), its associated levee and overbank
deposits develop in the intra-slope basin. The group
of contourite features comprises plastered drifts,
moats, elongated drift and sediment waves (Iglesias
2009; Van Roij et al., 2010). Three plastered drifts have
been mapped on the southern wall, one in the west
and two in the eastern part. The Le Danois moat runs
along the foot of the southern wall and leads into the
Le Danois turbidity channel. Associated to this moat,
there is an elongated drift developed over the intraslope basin.
Genetic processes
The Le Danois Bank was previously formed as a
horst, through rifting and subsidence from the
Triassic to Upper Cretaceous), and was later uplifted
by means of several northwards thrusts between the
northern base of this bank and the continental shelf
during the period of compressive deformation from
the Paleocene to the Oligocene (Gallastegui et al.,
2002). The pre-Mesozoic basement and Mesozoic
sedimentary rocks outcrop at the top of the bank
forming a monoclinal series dipping toward the south
(Boillot et al., 1974; Alvarez-Marrón et al., 1997). Posttectonic gravitational processes smoothed the relief
during the Neogene-Quaternary (Boillot et al., 1974).
The uplift of the Le Danois Bank mainly took place
during the Tertiary compression, although its current
configuration is the result of recent tectonic readjustments. Some of these readjustments were produced
by diapirism and subsidence in the Asturian
Intraslope Basin which may also have entrapped the
sedimentary input coming from the continental shelf
(Boillot et al., 1979). Diapirism has also affected the
basement highs of the intraslope basin (Leprêtre,
1974; Iglesias, 2009). Biogenic constructions have
been observed on this seamount (Sanchez et al.,
2008; 2009). The main sedimentary processes affecting this seamount include downslope processes
(mainly mass movements) and alongslope processes
principally related to the MOW (Fig. 2) (Van Rooij et
al., 2010). Mass transport is suggested by the presence of slide scars, gullies, and mass movement
deposits on the flanks. Many of these mass-transport
deposits evolve into gravity flows favouring the incision of gullies: on the northern wall they can reach
the continental rise where they generate depositional
lobes, and on the southern wall they are canalised
around the bank inside the Le Danois turbidity channel at the foot of the bank (Ercilla et al., 2008a;
Iglesias, 2009; Van Rooij et al., 2010) (Fig. 10). The
alongslope processes are represented by plastered
drifts and moat elongated drifts (Iglesias, 2009; Van
Rooij et al., 2010). When the MOW reaches the
Asturian Marginal Plateau it is divided into three
branches, interacts with the Vizco High and the Le
Danois Bank, and is capable of reworking the gravity
deposits of the bank and the shallower part of the
intra-slope basin to create the moat and associated
drifts along the foot of the bank.
506
Figure 10. The Le Danois Bank of the Cantabrian margin: (A) Seismic profile showing the architectural features and (B) Bathymetric map
showing the geomorphological features. Modified from Iglesias, (2009).
Figura 10. Banco de Le Danois en el Margen Cantábrico: (A) Perfil sísmico mostrando los rasgos arquitectónicos del margen y (B) Mapa
batimétrico mostrando los rasgos geomorfológicos. Modificada de Iglesias, (2009).
Remarks on the compilation of Iberian seamounts
The compilation of Iberian seamounts describes
the geomorphology of 15 seamounts in the context of
the genetic and current morpho-sedimentary process
in six sectors around Iberia (Balearic Promontory,
Alboran Sea, Gulf of Cadiz, Western Portugal,
Galician Margin, and Cantabrian Margin). Other
seamounts are also shown in Figure 1 that will be
studied in the future. This compilation is not a complete synthesis of all the seamounts around Iberia but
an attempt to show that full advantage must be taken
of existing geological knowledge to provide an
overview of the main areas of seamount distribution.
On distribution and size. The majority of the
seamounts considered are located in the southern
(five seamounts) and eastern (three seamounts) areas
of Iberia, with two seamounts from the Gulf of Cadiz,
three from the Atlantic oceanic domain (southwest
and west of Iberia) and two on the continental margins of north-western and northern Iberia. In the
future it is hoped that further knowledge will be gathered on the Atlantic oceanic domain seamounts,
which are numerous and varied in the vicinity of the
507
Horseshoe Abyssal Plain and close to the Tore Smt.,
and the Bay of Biscay. The seamounts can be divided
into two groups based on size: i) those less than 20
km long, basically those studied on the
Mediterranean margins; and ii) those longer than 50
km, corresponding to those studied on the Atlantic
margins, with the exception of the Guadalquivir Bank.
The width of these seamounts ranges between 7.5
and 25 km, apart from the Tore Smt. which exceeds
100 km, and the Galicia Bank, Gorringe Bank and
Coral Patch Smt. which are wider than 50 km, probably in all four cases due to their geological complexity. However, it is worth noting that the length/width
ratio is, in most cases, between 1 and 2, with the
exception of the Alboran Ridge and Portimao and Le
Danois banks, probably due to the linear nature of
their tectonic origin.
The area occupied by all the seamounts varies
greatly and includes the exceptional Tore Smt.
(31,000 km2), the Gorringe Bank (14,000 km2) and
Coral Patch Smt. (8,400 km2). The remaining highs
can be divided into two groups: those with an area
greater than 1,000 km2 (Alboran Ridge, Le Danois,
Galicia and Portimao banks) and those with an area of
50 to 200 km2 (all the Mediterranean seamounts apart
from the Alboran Ridge, and the Guadalquivir Bank).
This parameter again points to geological and tectonic complexity as determining factors. There is a general difference between the Mediterranean
seamounts (Balearic Promontory and Alboran Sea),
which are smaller and distributed in specific clusters,
and the Atlantic seamounts (southwest, west, northwest and north Iberia), which are bigger and associated with large crustal elevations of volcanic and/or
tectonic origin. The exception is the Alboran Ridge
because of its great length and elevation.
On scientific knowledge. The Iberian seamounts
are first-order morphological elements in the sedimentary evolution of continental margins and the
adjacent oceanic domains. These seamounts are
numerous and varied, and together they constitute a
fair representation of the global diversity of these features. Most of the submarine elevations are structural in origin and their most recent reliefs are related to
the different compressive stages that have affected
Iberia since the Eocene. Volcanic seamounts are
underrepresented in this region, although they are
the most common globally. The location, distribution
and morphogenetic evolution of the seamounts
around Iberia clearly reflects the tectonic evolution,
including the geodynamic context where these structures are located (in the case of the most western feature), as well as the consequence of compressive
episodes in Iberia since the Eocene. This highlights
the importance of tectonic reactivation in the area. A
Pliocene-Quaternary reactivation can be observed in
the Balearic Promontory (Emile Baudot Smt.), and the
Alboran seamounts (especially on the Alboran
Ridge), as well as in the Coral Patch Smt., Gorringe
Bank, Tore Smt., Guadalquivir Bank and Portimao
Bank, where deformation is also related to diapirism.
Miocene reactivation, however, is responsible for the
latest uplift of the Galicia and Le Danois banks. In this
sense, tectonic reactivation of relief is more recent to
the south of Iberia as the distance to the active plate
boundary between Africa and Eurasia decreases.
The presence of seamounts on continental margins and in ocean basins, both past and present, has
favoured the development of a series of sedimentary
processes: i) the formation of slope failure and landslide deposits (Gorringe Bank, Alboran Ridge), partly
caused by steep slopes due to tectonic reactivation of
relief, ii) interference with water mass dynamics generating the bottom currents associated with contourite systems (Djibouti Banks and Galicia Bank) and
specific features of regional contourite systems
(Guadalquivir Channel associated to the Guadalquivir
Bank); iii) specific habitat generation due to the high
dynamics associated with seamounts, especially
cold-water coral reefs (Coral Patch Smt, Galicia and
Le Danois banks); and iv) development of isolated
shelves where the summits are located at a water
depth of less than 100 m, with erosive terrace levels
related to sea level changes and carbonate sedimentation characterised by maërl carpets (Alboran Ridge,
Ausiàs March and Emile Baudot seamounts).
On the next steps for seamount science. In order to
continue making relevant scientific discoveries, it is
important to consider the most exciting and significant research topics. Which new approaches and
technologies will give the highest return for the
investment of research time? As in other fields where
complex systems are involved, seamount science
depends on the effective integration of multidisciplinary science and research coordination. Although
certain special features have received a great deal of
attention, many fundamental questions regarding the
nature of seamount processes remain unanswered.
Acknowledgements
This work was funded by the projects “Seamounts of
the southern Iberia: tectonics and sedimentation project (MONTERA-CTM2009-14157-C02-01-02)” and
“Erosive features and associated sandy deposits generated by the Mediterranean outflow water around
508
Iberia (MOWER- CTM2012-39599-CO3-03)” of the
Spanish R & D Plan (MINECO). We thank IHS for supporting us with the Kingdom Suite Program. We also
extend our thanks to the Minister of the Environment
and Rural and Marine Affairs (Secretaria General del
Mar) for some of the bathymetric data used in this
study, as well as the Fundaçao para a Ciência e a
Tecnologia.
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Recibido: febrero 2014
Revisado: noviembre 2014
Aceptado: diciembre 2014
Publicado: junio 2015
514

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